Secondary mirror damage on new scope

[Jonny_H]

I have attached a photo of the old and new scopes in the hope that it will put my question into context.  The old original scope is the 'frosted' finish and the new replacement has the 'mirrored' finish.

Thanks,

Jon

[tooth_dr]

7 minutes ago, Jonny_H said:

I have attached a photo of the old and new scopes in the hope that it will put my question into context.  The old original scope is the 'frosted' finish and the new replacement has the 'mirrored' finish.

Thanks,

Jon

Whats the other side like?  Dare I ask is it frosted 🤣

 

[Jonny_H]

😂 a very valid question and one i asked myself and rather promptly checked.......I am pleased to say that the primary mirror is mirrored inside.  So at the very least it isn't back-to-front!

[Carbon Brush]

A strange mirror indeed. Well actually no it isn't. I have one in the bathroom. A shaving mirror. One side flat, the other magnifying.

The reflective back means that stray light behind the scope will have much less chance of entering the tube and affecting the viewing experience.

You may be on to an idea here.....

[NGC 1502]

That’s really weird, never seen a mirror aluminised BOTH sides, lets hope it’s a whole lot better than a shaving mirror.....

Are you ok with that, even if it performs as it should ?

Ed.

 

[Jonny_H]

7 minutes ago, NGC 1502 said:

That’s really weird, never seen a mirror aluminised BOTH sides, lets hope it’s a whole lot better than a shaving mirror.....

Are you ok with that, even if it performs as it should ?

Ed.

 

I dont really know to be honest. I guess if it doesnt impact performance I will be ok with it. There must be a technical reason why the back is 'normally' frosted. 

I haven't been very lucky with this scope  have I!? 😕

Edited June 9, 2020 by Jonny_H

[Peter Drew]

Are you sure there is a coating on the rear face?, if the substrate that the mirror was made from was some form of float glass then it could well be that it had a polished surface on both sides initially.  In that case, you would be able to see the rear surface of the optical side through the back of the mirror.  If it actually has been aluminised on both sides it will have no detrimental affect on the performance, in fact it has been proposed in the past that doing so could improve the rate of cooling.  I've never known of this being done however, maybe the added cost was not in proportion to the benefit.     🙂  

[markse68]

It’s gotta be just polished glass as you can see the whole cork supporting pad in the reflection. I guess if the blanks have such perfect finish why do they bother frosting them? Maybe that’s the question they asked themselves also  

[Jonny_H]

6 minutes ago, markse68 said:

It’s gotta be just polished glass as you can see the whole cork supporting pad in the reflection. I guess if the blanks have such perfect finish why do they bother frosting them? Maybe that’s the question they asked themselves also  

This is what I am asking myself. To be honest I think it looks quite cool and it's different! As long as performance isnt impacted I'll be happy with it. But it begs the question as to why they are frosted in the first place!

Edited June 9, 2020 by Jonny_H

[markse68]

5 minutes ago, Jonny_H said:

This is what I am asking myself. To be honest I think it looks quite cool and it's different! As long as performance isnt impacted I'll be happy with it. But it begs the question as to why they are frosted in the first place!

Maybe they only frost the ones that get marked during the grinding/polishing and don’t look so good and those that survive in a pretty state get left. So your new one was handled better in the factory. Or maybe they got a new supplier of blanks 🤷‍♂️

Edited June 9, 2020 by markse68

[Jonny_H]

14 minutes ago, markse68 said:

Maybe they only frost the ones that get marked during the grinding/polishing and don’t look so good and those that survive in a pretty state get left. So your new one was handled better in the factory. Or maybe they got a new supplier of blanks 🤷‍♂️

Yes it could be a number of reasons!

[Oldfort]

5 hours ago, merlin100 said:

Should or shouldn't?🤔

Shouldn't.  Apologies for that.

[wheresthetorch?]

That is quite odd.

Could it be that the frosting isn't actually on the back of the mirror but is a separate cover to protect it? In which case it could be missing on yours? Maybe someone with the same scope could check for you. 

[dweller25]

19 hours ago, Jonny_H said:

I have attached a photo of the old and new scopes in the hope that it will put my question into context.  The old original scope is the 'frosted' finish and the new replacement has the 'mirrored' finish.

Thanks,

Jon

You do right to send the first scope back - it’s stands out as very different to normal.

[Neil H]

This may sound stupid but if they polished it then did not pass a test  to not waste the unit they polished the other side . It does look strange , skywatcher is owned by Celestron so the blanks may come from different company now 

If your worried about stray light getting in the back you can always put a dark shower cap over that end to see if it makes a difference

[CraigT82]

I agree that its the back side of the coatings on the front of the mirror that you can see from the back, as opposed to the actual back of the mirror being coated.

I shouldn't think it's any problem. If it bothers you a half hour with some wet and dry wi give you a nice frosting! 

[Louis D]

Very cool looking effect.  Now your scope is unique and you can ask for a premium sales price should you ever decide to sell it. 😉

Edited June 10, 2020 by Louis D

[Jonny_H]

7 hours ago, wheresthetorch? said:

That is quite odd.

Could it be that the frosting isn't actually on the back of the mirror but is a separate cover to protect it? In which case it could be missing on yours? Maybe someone with the same scope could check for you. 

I do still have the old one in my possession as I am still waiting for the courier to collect it.

I guess I could have a look myself to see if it is a separate cover  but am worried about damaging it as I am not very familiar with how the scopes are put together.

 

Edited June 10, 2020 by Jonny_H
Added another quote to comment on

[Jonny_H]

51 minutes ago, Louis D said:

Very cool looking effect.  Now your scope is unique and you can ask for a premium sales price should you ever decide to sell it. 😉

There is that side to it!

[Peter Drew]

I have a 8" mirror with a polished finish on the back surface, it does look at first glance that it has been coated.  Although a frosted rear surface could be applied to a scratched polished surface to eliminate the scratches, the more usual reason is to flatten the back surface of moulded blanks.    🙂

[Jonny_H]

2 hours ago, Peter Drew said:

I have a 8" mirror with a polished finish on the back surface, it does look at first glance that it has been coated.  Although a frosted rear surface could be applied to a scratched polished surface to eliminate the scratches, the more usual reason is to flatten the back surface of moulded blanks.    🙂

Hi Peter,

I assume you mean you have a scope with the same polished mirror on the back as mine? If so have you noticed any issues with it? 

Regards,

Jon

[discardedastro]

3 hours ago, Peter Drew said:

I have a 8" mirror with a polished finish on the back surface, it does look at first glance that it has been coated.  Although a frosted rear surface could be applied to a scratched polished surface to eliminate the scratches, the more usual reason is to flatten the back surface of moulded blanks.    🙂

Yeah, the frosting is just a byproduct of polishing to flatten the back of the moulded blank and thus get it sitting flat in the mirror cell. I'd be a little concerned about a primary that hadn't been flattened, myself.

[Jonny_H]

13 hours ago, discardedastro said:

Yeah, the frosting is just a byproduct of polishing to flatten the back of the moulded blank and thus get it sitting flat in the mirror cell. I'd be a little concerned about a primary that hadn't been flattened, myself.

Hmmm.....I feel like I am back to square one again and not knowing what to do for the best.  I haven't had a chance to use the scope properly yet as the weather has been shocking lately.

As previously mentioned I have emailed the shop i originally purchased the scope from and have also attached photo's of the back of both original and replacement so keen to get there views.

I am starting to feel like I have been rather unlucky with this scope!  

[banjaxed]

As there are only 3/4screws holding the primary mirror could you ask the supplier if you could just swap them ?

[Jonny_H]

9 minutes ago, banjaxed said:

As there are only 3/4screws holding the primary mirror could you ask the supplier if you could just swap them ?

Yes that it what I was thinking.  I will wait for a response from them then pose that question.

I havent done anything like this before but if they say that is fine - how 'easy' is it to swap the assembly over?  Is it an easy DIY job?